One of a semiconductor device for power includes an IGBT (Insulated Gate Bipolar Transistor) having a trench gate structure. When the IGBT is used as a switching element, it may be desired that its on resistance is low and switching is fast. In the IGBT, since a pitch of a trench gate is shortened, a resistive component of a semiconductor region between trench gates becomes large, so that a so-called IE effect (Injection Enhanced) occurs. In this way, an on voltage becomes small. The IE effect also occurs when providing a barrier region for a carrier between the trench gates.
However, when the IE effect occurs by such a method, a carrier concentration of an emitter side may increase. In this way, during turn-off, since carriers are not quickly discharged to the emitter side, it is probable that switching loss during turn-off increases. As described above, there is a trade-off relation between reduction of an on voltage and reduction of switching loss during turn-off.